Processes in the graphic arts require the use of an image forming system having a very high contrasty photographic characteristic, particularly one with a gamma (.gamma.) of 10 or more, in order to attain faithful reproduction of halftone images or line drawing images by means of dot images.
This object has heretofore been achieved by using a specialized developing solution generally referred to as a lithographic developer. The lithographic developer contains hydroquinone as the sole developing agent and, in order to ensure the desired infectious development, a sulfite is used as a preservative in the form of adduct with formaldehyde so that the concentration of free sulfite ions is held very low, typically no more than 0.1 mole per liter. This lithographic developer however has a serious defect in that it is easily oxidized by air, and, consequently, it cannot be stored any longer than 3 days.
One conventional method for attaining a high-contrast photographic characteristic using a stable developing solution relies on the use of hydrazine derivatives as disclosed in U.S. Pat. Nos. 4,224,401, 4,168,977, 4,166,742, 4,311,781, 4,272,606, 4,211,857 and 4,243,739. This method provides supercontrasty and high-speed photographic characteristics and has the advantage of permitting the incorporation of a sulfite in the developing solution in high concentrations, with the result that the developing solution is rendered much more stable to aerial oxidation than the lithographic developer. However, this improved image forming system, capable of achieving a markedly high-speed and contrasty characteristic, causes "black spots" due to infectious development, which is quite undesirable for the purpose of attaining good results in process photography. These black spots, also known as "black pepper", occur in the areas between dots, which areas should not be developed, and their occurrence increases as a result of prolonged storage of the photographic material, especially when subjected to a hot and humid atmosphere. If the developing solution is exhausted as a result of repeated use, the level of sulfite ions in the preservative is lowered and its pH increased, and this is another cause of frequent occurrence of "black pepper". Since light-sensitive materials with "black pepper" have a very low commercial value and are not really suitable for use in process photography, considerable efforts have been made to eliminate this problem. However, a light-sensitive material having reduced "black pepper" often suffers from a degraded sensitivity and gamma (.gamma.) characteristic, and is also undesirable for commercial use. A strong need has therefore existed for providing an image-forming system that has reduced "black pepper" without compromising the desirable high-speed and contrastive photographic characteristic.